Synthesis on the Shear Wave Velocity of Engineering and Seismic Bedrocks in Northern Algeria based on Recent Experimental Investigations

Abstract

In the field of civil engineering, knowledge of good rocky ground resistant to collapse minimizes the level of seismic risk, often known as the “engineering bedrock”. In lithology, it overlays a harder rock known as “seismic bedrock”. The latter is a transition zone between the earth's crust and the surface layers. It is sometimes impossible to carry out deep drilling and investigation techniques to define the engineering substratum for the foundations; in this case we rely on the seismic regulations. In Algeria, after the 2003 Boumerdès earthquake, seismology studies were expanded in order to better understand the Algerian crust on both the marine and continental sides. Furthermore, studies on seismic risk reduction in urban environments are increasingly focusing on the phenomenon of site effects or local amplification. Several experimental studies conducted in Algeria as part of seismic microzoning programs have defined the existence of these two substrate interfaces by identifying the natural frequencies of the ground. In this work, we describe the findings of numerous key research that reached the seismic bedrock in Algeria. It is classified as having two geological natures: Mesozoic with a shear wave velocity, Vs, less than 3000 m/s, and metamorphosed Paleozoic with Vs greater than 3500 m/s.